Particle counting immunoassay (PACIA)

Natural killer cell activation after infection with lactate dehydrogenase-elevating virus

Early after infection, lactate dehydrogenase-elevating virus (LDV) alters the immune system by polyclonally activating B lymphocytes, which leads to IgG2a-restricted hypergammaglobulinaemia, and by suppressing the secretion of Th2 cytokines. Considering that these alterations may involve cells of the innate immune system and cytokines such as interferon-gamma (IFN-gamma), we analysed the effect of LDV on natural killer (NK) cells. Within a few days of infection, a strong and transient NK cell activation, characterized by enhanced IFN-gamma message expression and cytolysis, was observed. LDV triggered a large increase in serum IFN-gamma levels. Because NK cells and IFN-gamma may participate in the defence against virus infection, we analysed their possible role in the control of LDV titres with a new agglutination assay. Our results indicate that neither the activation of NK cells nor the IFN-gamma secretion affect the early and rapid virus replication that follows LDV inoculation.

Synergistic proliferation and activation of natural killer cells by interleukin 12 and interleukin 18

We investigated the effects of IL-12 and IL-18 on unstimulated murine splenocytes and observed that the two cytokines strongly synergized for their proliferation, whereas IL-12 and IL-18 alone were essentially inactive in this respect. Phenotypical and functional analyses of cells proliferating in response to IL-12 and IL-18 revealed that large granular Ly-49C(+)DX5(+)CD3(-)NK blasts were expanded in these cultures and that they displayed cytotoxic activity against Yac-1 cells, a murine NK cell target. Further analyses indicated three major differences between NK cells appearing in response to IL-12 and IL-18 and those derived in the presence of other NK cell growth factors, such as IL-2 or IL-15. First, a population of T-NK cells, i.e. expressing T cell (TCRalphabeta, CD3) and NK cell (Ly-49) markers, was detected amongst cells growing in IL-2 or IL-15 but not in cultures supplemented with IL-12 and IL-18. Second, most NK cells derived with IL-2 or IL-15 expressed the NK1.1 antigen, while those derived with IL-12 and IL-18 did not. Finally, striking differences were observed regarding cytokine production. Cells stimulated with IL-12 and IL-18 in combination, but not with IL-2 or IL-15, produced IFN-gamma, IL-3, IL-6 and TNF. IFN-gamma was not involved in the response of NK cells to IL-12 and IL-18, as indicated by experiments demonstrating that the combination of the two cytokines displayed similar effects on spleen cells from IFN-gammaR-knock-out mice. Receptor (IL-12Rbeta1, IL-12Rbeta2 and IL-18R) gene expression studies did not indicate that the mechanism underlying the synergy between IL-12 and IL-18 involved reciprocal induction of their receptors. Taken together, our results demonstrate that IL-12 and IL-18 exert striking synergistic activities for NK cell proliferation and activation, distinct from those induced by IL-2 or IL-15.

Inhibition of in vitro immunoglobulin production by IL-12 in murine chronic graft-vs.-host disease: synergism with IL-18

We investigated the effects of IL-12 on immunoglobulin (Ig) production in vitro in murine chronic graft-vs. -host disease (cGVHD), a lupus-like model of overt B cell activation induced by allogeneic stimulation. Addition of IL-12 to cGVHD splenocytes strongly inhibited total Ig (Igkappa), IgM and IgG1 production. Although IL-12 down-regulated IL-4, IL-5, IL-9 and IL-10 production, its inhibitory activity on Ig production could not be ascribed to down-regulation of these cytokines, as addition of saturating doses of IL-4, IL-5 and/or IL-9 did not reverse the inhibitory activity of IL-12. Interestingly, IL-12 was also found to suppress the stimulating effect of IL-4 and IL-5 on Ig synthesis by cGVHD splenocytes. Several lines of evidence indicated that the inhibitory activity exerted by IL-12 on Ig production was mediated by IFN-gamma. First, IFN-gamma was produced in large amounts upon IL-12 stimulation. Secondly, it displayed a potent inhibitory activity on Ig production. Thirdly, Ig production was also inhibited by IL-18, a recently cloned IFN-gamma-inducing cytokine. Finally, the inhibitory activity of IL-12 was blocked by anti-IFN-gamma monoclonal antibody. We also investigated whether IL-12 down-regulated Ig production by purified cGVHD B cells. We found that IL-12 had only a marginal inhibitory activity on highly purified B cell populations isolated from cGVHD splenocytes and stimulated with IL-4 and IL-5, and that IL-18 was inactive in this respect. However, when the two cytokines were combined, a striking synergy was unmasked not only for IgG1 inhibition but also for IFN-gamma production by these B cell populations. Taken together, our results demonstrate that IL-12 inhibits in vitro Ig production by activated splenocytes through IFN-gamma production and that it synergizes with IL-18 on activated B cells to inhibit Ig production, through up-regulation of IFN-gamma production by B cells.

Particle counting assay for anti-toxoplasma IgG antibodies. Comparison with four automated commercial enzyme-linked immunoassays

An assay for anti-toxoplasma IgG antibodies based on agglutination of latex particles was set up and compared with commercial immunoassays. The reaction was measured by instrumental counting of particles remaining unagglutinated. The running time was 45 min. This test (PaC) was compared using 243 serum samples with four automated commercial immunoassays: the Enzymum test Toxo IgG (ES300, Boehringer), the Vidas Toxo IgG (Biomérieux), the IMX Toxo IgG (Abbott), the Magia Toxoplasma gondii IgG (Merck). The mean values (+/- SD) obtained by IMX (25 IU +/- 68) and ES300 (45 IU +/- 142) were significantly lower than the values obtained by Vidas (73 IU +/- 237, p < 10(-4) and p = 0.006, respectively), by Magia (80 IU +/- 300, p < 10(-4) and p = 0.0005) and by PaC (70 IU +/- 260, p < 10(-4) and p = 0.0126). The correlations between PaC and Toxo IgG Boehringer, Biomérieux, Abbott, Merck were r = 0.97, r = 0.98, r = 0.94, r = 0.98, respectively. The correlation coefficients between the enzyme-immunoassays ranged from 0.96 to 0.99. All positive samples by PaC were found to be positive by enzyme-immunoassays except for eight sera which were doubtful positives by the Enzymum test ToxoIgG from Boehringer. No negative sample by PaC was found positive by any of the enzyme-immunoassays. In PaC, when two latex preparations coated with different antigen were compared, the correlation was rather weak (r = 0.93) suggesting that the selection of the antigen can be critical. In conclusion, the four automated commercial immunoassays now available gave similar results. However, the discrepancies observed in this study underlined the importance of clinical and biological follow-up of the patients and the necessity to confirm the result. The introduction of a new technique such as PaC, which is now available for a large variety of assays in Clinical Chemistry and Microbiology, is justified by its intrinsic advantage of homogeneity. Therefore, automation is easy as well as the control of possible interference.

Evaluation of monoclonal antibodies with specificity for human IgA, IgA subclasses and allotypes and secretory component. Results of an IUIS/WHO collaborative study

51 monoclonal antibodies (McAb) with putative specificity for human IgA, the IgA subclasses, Am allotypes or secretory component (SC) were evaluated for immunoreactivity and specificity by nine laboratories employing immunodiffusion, agglutination, immunohistological assays, immunoblotting and direct binding and competitive inhibition enzyme immunoassays. McAbs specific for IgA PAN (n = 24), IgA1 (n = 7), IgA2 (n = 3), IgA2m(2) (n = 2), non-IgA2m(2) (n = 4) and SC or secretory IgA (n = 5) were identified that were immunoreactive and specific in the assays employed. The McAbs identified as IgA- or SC-reactive were shown to be non-reactive to human IgG, IgM, IgD, IgE, kappa and lambda by direct binding and competitive inhibition immunoassays. Interestingly, no McAbs with restricted specificity for IgA2m(1) were identified. Some McAbs displayed higher affinity and/or better performance in one or several of the assay groups. The IgA- and SC-specific McAbs identified in this international collaborative study have potential as immunochemical reference reagents to identify and quantitate monomeric and polymeric IgA in human serum and secretions.

Influence of running different distances on renal glomerular and tubular impairment in humans

Strenuous exercise has been claimed to modify renal glomerular and tubular function, the relative involvement of the two sites being unknown. These changes may be assessed by the determination of plasma high and low molecular mass proteins. A group of 13 man performed five runs (100, 400, 800, 1,500, 3,000 m) at maximal speed. The excretion rates and renal clearances of creatinine, albumin (Alb), beta 2-microglobulin (beta 2-m) and retinol-binding protein (RBP) were determined before and after each run. The glomerular filtration rate remained stable during the shorter runs and declined by about 40% during the longer runs. The excretion rate for Alb rose from 10-fold above the basal value (6 micrograms.min-1) for the 100 m to 49-fold for the 800 m and then declined for distances up to 3,000 m. The beta 2-m and RBP had a lesser initial increase, 3.5-(rest 55 ng.min-1) and 7.6-(rest 116 ng.min-1) fold, respectively, for the 100 m run and thereafter showed a higher excretion rate than Alb for the 400 m and 800 m runs. The renal clearances of these high (Alb) and low molecular mass (beta 2-m and RBP) proteins followed the changes observed for excretion rates. There was a linear relationship (r2 = 0.996) between plasma lactate concentration and total protein excretion in the postexercise period when taking all five runs into consideration. Glomerular permeability was primarily affected by the 100-m run while the longer runs modified both the glomerular and the tubular sites. To conclude, the present study demonstrated a differential response of the kidney to strenuous exercise with respect to the intensity and duration of the events.

Detection of mycobacterial antigens present in short-term culture media using particle counting immunoassay

Particle counting immunoassay (PACIA) was compared with the BACTEC system for detecting mycobacterial growth after short-term culture and was used to identify M. tuberculosis. The latex particles were coated with polyclonal anti-BCG or with specific 2A1-2 monoclonal antibodies. Bottles containing nonradioactive Middlebrook 7H9 liquid medium and BACTEC 12B vials were inoculated with equal amounts of mycobacteria from four reference strains (M. tuberculosis, M. kansasii, M. avium, and M. xenopi). Using anti-BCG, PACIA detected mycobacterial antigens 3 to 6 days before the BACTEC system. M. tuberculosis was differentiated from the other mycobacteria using 2A1-2. Seventeen clinical samples were also studied. In the same 10, the two techniques detected mycobacteria, PACIA with anti-BCG after 9 days and BACTEC 1 to 5 days later. For 9 of the 10 samples, PACIA with 2A1-2 detected M. tuberculosis after 20 days, a result confirmed with the AccuProbe system. M. xenopi was biochemically identified in Specimen 10. Nonmycobacterial diseases were diagnosed in the 7 remaining unreactive specimens. We conclude that PACIA detects mycobacterial growth earlier than BACTEC and that M. tuberculosis can be distinguished from other mycobacteria in PACIA performed with specific monoclonal antibodies.

Characterization of an anti-idiotypic MoAb bearing an internal image of the receptor-binding epitope of cholera toxin

A mouse anti-cholera toxin (CT) MoAb, mAb1, specific for the GM1-binding epitope of CT, was used to raise a syngenic anti-idiotypic MoAb, mAb2. Purified mAb2 was specific for mAb1 as shown by latex particle counting immunoassay and ELISA. Several experiments of competition between mAb2 and CT for binding to mAb1 demonstrated that mAb2 bore an internal image of the GM1-binding epitope of CT. Binding of mAb2 to GM1 unambiguously corroborated the mAb1-paratopic specificity of mAb2. Furthermore, mAb2 acted as a CT-surrogate antigen: rabbits injected with mAb2 produced some anti-CT antibodies, Ab3, which resembled mAb1 in specificity as expected. The potential use of this mAb2 as vaccine or as prophylactic agent to prevent CT from binding to its cellular receptor is discussed.

Latex agglutination assay of human immunoglobulin M antitoxoplasma antibodies which uses enzymatically treated antigen-coated particles

An assay of immunoglobulin M (IgM) antitoxoplasma antibodies which is rapid (less than 30 min), homogeneous, and reliable (interassay coefficient of variation, less than 11%) is proposed. Its principle is based on the observation that a suspension of latex particles coated with toxoplasma antigens, after treatment with proteinase K, becomes less agglutinable by IgG antibodies but more agglutinable by IgM antibodies. The difference between the activities of the two classes of antibodies is increased by the addition of a monoclonal antibody directed against the Fc region of IgM. Agglutination is measured with a special instrument which optically counts the particles that remain free after the reaction. Turbidimetric reading, although less sensitive, is also suitable. No significant interferences either by IgG antitoxoplasma antibodies or by rheumatoid factor or antinuclear antibodies were observed. The sensitivity was similar to that of the immunosorbent agglutination assay.

Measurement of serum myoglobin by a turbidimetric latex agglutination method

We evaluated an immunoturbidimetric quantitation for serum myoglobin by the latex agglutination method using an automated biochemical analyzer. This method is rapid, specific, accurate, precise, and has wide dynamic range. The total assay time is 10 min and is performed at 37 degrees C with continuous monitoring at 570 nm. The assay results were compared with radioisotopic immunoassay results and showed a good correlation coefficient, r = 0.99; Y = 0.98 x + 9.3; N = 79. Sera from healthy adults has a myoglobin concentration in the range of 15-80 ng/ml(N = 362). Sex- and age-related differences were observed. The serum myoglobin levels in males and elderly people showed higher concentration than in females and younger people. The peak elevation of serum myoglobin compared with other cardiac markers was observed within 6 hours after onset of chest pain as well as the CK-isoform ratio (MM3/MM1). All of the serum from 21 patients with definite acute myocardial infarction showed increased serum myoglobin levels (100-1200 ng/ml) upon admission and within 6 hours. The results suggest that assays for serum myoglobin levels are helpful in the early diagnosis of acute myocardial necrosis.

Automated quantitative nephelometric latex immunoassay for determining ferritin in human serum

We describe a rapid and sensitive latex nephelometric immunoassay for quantifying ferritin in human serum. This latex immunoassay procedure uses commercially available ready-for-use reagents [Tina-Quant (a) Ferritin, Boehringer Mannheim] that have a long shelf life. The assay consists of incubating the diluted serum sample (5-fold) for 12 min at room temperature with latex particles covalently coated with anti-ferritin antibodies, and then quantifying the change of light-scatter produced. The assay is fully automated on the Behring nephelometer analyzer with a sampling rate of 150 samples/hour. The method has an analytical range of 3 to 260 micrograms/l. Maximal intra- and inter-assay CVs were 4.0 and 6.2%, respectively. Analytical recoveries ranged from 91.3 to 103.6%. Assay detection limit was less than 3 micrograms/l. Linearity of the test is given throughout the measuring range. There was no interference from bilirubin (up to 340 mumol/l), haemoglobin (up to 7 g/l), or rheumatoid factor (up to 1,100 IU/ml). Turbid and lipemic samples interfere. This interference may be avoided by pretreating these samples prior to assay. Results correlated well with those obtained by an automated ELISA test (r = 0.995) and with those of two commercial RIA methods (r greater than 0.97). This latex nephelometric procedure is a convenient method and represents an interesting alternative to other immunoassays for measuring ferritin in human serum.

Protection of rat intestine against cholera toxin challenge by monoclonal anti-idiotypic antibody immunization via enteral and parenteral routes

A mouse monoclonal anti-idiotypic (anti-id) immunoglobulin M (IgM) antibody, called MAb2, was raised against a mouse monoclonal anti-cholera toxin (anti-CT) antibody (MAb1). The MAb2 was shown, by competition with CT for MAb1, to bear the internal image of an epitope of CT. MAb2 immunization of rats was performed via the intraperitoneal, intragastric, and intrajejunal routes and compared with immunization of rats with either a control, isotype- and allotype-matched MAb or with CT via the same routes. Both serum IgG and bile IgA anti-CT Ab3's were detected by enzyme-linked immunosorbent assay in anti-id MAb2-immunized rats, although their titers were lower than those in CT-immunized rats. No anti-CT antibodies were detected in sera and bile of rats immunized with the control MAb. When tested for degree of gut protection against a CT challenge, rats immunized with MAb2 by the intrajejunal route showed a rather high degree of protection, which was only slightly lower than that of rats immunized with CT via the same route; all rats but one immunized with the control MAb were unprotected. There was, however, no correlation between serum or bile anti-CT titers and degree of gut protection in MAb2-immunized rats. Their serum anti-CT Ab3's were purified by adsorption and elution from a CT immunosorbent and resembled anti-CT MAb1 in their unique reactivity with MAb2. This constitutes to our knowledge the second report of protection against a pathogen by anti-id immunization via the enteric route.

The digoxigenin:anti-digoxigenin (DIG) technology--a survey on the concept and realization of a novel bioanalytical indicator system

A review is given on the novel non-radioactive digoxigenin:anti-digoxigenin (DIG) bioanalytical indicator system. After a general introduction on direct and indirect indicator systems based on previous non-radioactive indicator reactions as well as in vitro and in vivo amplification procedures the principle of the new digoxigenin:anti-digoxigenin technology is demonstrated. The novel system is based on the specific high-affinity interaction between the cardenolide digoxigenin from Digitalis plants and a digoxigenin-specific antibody coupled with a reporter group. A variety of methods for digoxigenin modification of nucleic acids, proteins and glycans are presented. In addition, various applications of the novel non-radioactive indicator system in a variety of direct or indirect detection approaches with either insoluble or soluble substrates are described. It is also shown that with these applications alternative reaction formats are used which are partly characterized by additional amplification steps.

Quantitative automated latex nephelometric immunoassay for determination of myoglobin in human serum

We have evaluated a new latex nephelometric test for the quantitation of myoglobin in human serum. The assay consists of incubating the diluted serum sample (20-fold) for 12 min at room temperature with latex particles covalently coated with anti-myoglobin antibodies and then quantifying the change of light-scatter produced. The assay is fully automated on the Behring nephelometer analyzer with a sampling rate of 150 samples/hour. There is no interference from bilirubin (up to 340 mumol/l), haemoglobin (up to 7,000 mg/l), or rheumatoid factor (up to 1,100 int. units/ml). Myoglobin standard curve extends from 20 to 380 micrograms/l. Assay detection limit lies around 6 micrograms/l. Coefficient of variation ranged from 2.7 to 7.6%. Correlation coefficient between latex immunoassay and an RIA method was 0.987, calculated from the assay of 37 samples. A statistically significant difference was found between the distribution for females and males. The serum level of myoglobin showed an age-dependent variation. Concentrations up to 60 micrograms/l are considered to be normal.

Particle counting immunoassay of choriogonadotropin using monoclonal antibodies

A latex particle immunoassay has been developed for the quantification of choriogonadotropin in human serum using two monoclonal antibodies specific for the beta-chain of the hormone. The assay, based on optical counting of monomeric particles, was achieved in 40 min and the calibration curve was linear between 10 and 200 IU/l. Intra- and interassay precisions at three different levels of the curve varied between 3.3 and 10.9%. The method was validated by comparison with two different radioimmunoassays and correlation coefficients of 0.97-0.99 were obtained.

Homogeneous latex immunoassay for thyroid hormone testing. Determination of thyroxine and triiodothyronine

We describe here two latex immunoassays for total thyroxine (T4) and total triiodothyronine (T3). These homogeneous 60 min assays are quantified by optically counting the monomeric particles remaining after agglutination. When precision is assessed, both methods display coefficients of variation of 3-7% for within-run assays and 4-10% for between-run assays. The accuracy of the methods, as tested by dilution and spike recovery experiments, was found to be satisfactory. Two correlation studies were carried out to compare the present method with leading commercial methods. The coefficients obtained were: r = 0.92 and r = 0.93 with 150 sera for T3, and r = 0.95 (150 sera) and r = 0.93 (108 sera) for T4.

Immunological detection of mycobacterial antigens in infected fluids, cells and tissues by latex agglutination. Animal model and clinical application

We devised an immunoassay for the detection of mycobacterial antigens in cell lysates and in tissue extracts which is based on the agglutination of latex particles coated with anti-Mycobacterium bovis F(ab')2, followed by counting of non-agglutinated particles. Mycobacterium bovis cell lysates were tested and a reference curve was established, having a lower limit of detection of 15-20 Mycobacteria. We were able to detect mycobacterial antigens in cell lysates from bronchoalveolar washings and in spleen and liver lysates obtained from experimentally infected rabbits. Antigens were also detected in ten out of 11 samples obtained from patients with proven tuberculous infection. These samples were readily distinguished from 32 negative control samples after pepsin treatment. In contrast, periodate treatment of samples to destroy carbohydrate, abolished all reactivity. Following gel filtration chromatography we identified three peaks with antigenic properties in samples of all types. The detection of mycobacterial carbohydrate antigens by latex agglutination and particle counting should be a useful adjunct in the diagnosis of tuberculosis.

Immunoassay of theophylline by latex particle counting

We set up an immunoassay by particle counting for theophylline. Theophylline concentration is assayed by its capacity to inhibit the agglutination of theophylline coated latex particles by a specific monoclonal antibody, the agglutination being enhanced by a rabbit anti-mouse IgG antiserum. The dose range is 2-64 mg/L. The cross-reactions observed with caffeine (0.3%), theobromine (0.2%), 3-methylxanthine (0.7%) and 8-chlorotheophylline (2%) are very good when compared with other published methods. Within and between-run precisions measured at low, medium and high level of the calibration curve show coefficients of variation ranging from 3.9% to 9.5%. Our assay was correlated with the Fluorescence Polarization Immunoassay (FPIA) and a correlation coefficient of 0.96 was determined for 89 samples.

Interference of complement with the binding of carcinoembryonic antigen to solid-phase monoclonal antibodies

Six mouse monoclonal antibodies against carcinoembryonic antigen were evaluated for use in a solid-phase immunometric assay. Three IgG2 antibodies, when attached to polymer particles or microtiter wells, were found to be severely inhibited by fresh serum. The remaining three antibodies, which were of the IgG1 subclass, were inhibited only slightly or not at all when used in the same way. With the aid of labelled antibodies against C1q and C3, it was shown that antibody inhibition was accompanied by the binding of large amounts of these complement factors. Experiments involving heat inactivation or dilutions of serum, or the addition of EDTA, consistently revealed the same correlation between binding of complement factors and inhibition of CEA binding to antibody. It is suggested that the significant inhibition of the solid-phase IgG2 antibodies was caused by classical pathway activation of complement by the solid-phase antibody even in the absence of antigen. The slight inhibition of solid-phase IgG1 antibodies observed at high serum concentrations was probably due to complement binding by the alternative pathway. Preliminary evidence suggests that complement interference is not restricted to CEA assays, but is a potential problem in all types of serum immunoassays using solid-phase antibodies.

Immunoassay by particle counting for coagulation testing: application to the determination of antithrombin III, von Willebrand factor antigen (vWF:Ag) and plasminogen

Based on immunoassay by particle counting, three methods for antithrombin III, von Willebrand factor and plasminogen were developed on an automated IMPACT machine and on a semi-automated MULTIPACT system. Precision of the techniques, measured at low, medium and high level of the calibration curve showed coefficients of variation varying from 4.3 to 13.8%. Accuracy was evaluated by dilution recovery test and by correlation with rocket immunoelectrophoresis and chromogenic substrate techniques. The results show that the proposed methods correlate well with existing techniques and that immunoassay by particle counting is applicable to several coagulation tests.

A rabies agglutination test (RAT) for rabies antibody detection

An agglutination test has been developed for the detection of rabies antibodies after human vaccination. The rabies agglutination test (RAT) is based on the capability of specific antibody to agglutinate sensitized polystyrene (or latex) beads. In the RAT, latex beads were coated, in a first step, with inactivated and purified rabies virus (PV strain adapted and propagated on BHK-21 cells) and, in a second step, with bovine serum albumin. Negative control beads were coated with bovine serum albumin (BSA) only. To test for human antibody, several microliters of serum were mixed on a glass slide with an equal volume of virus-sensitized beads and the mixture was gently agitated. After a few minutes, agglutination was visible with sera which had been characterized as positive by the virus neutralization antibody (VNAb) technique. No agglutination was observed with negative sera tested with virus-coated beads or with positive sera tested with BSA-coated beads. Virus-sensitized beads were agglutinated when the virus neutralizing antibody titres were equal to or greater than 2.5 international units per ml (IU/ml) in human sera. The concordance between the RAT results and VNAb titres was about 97% when 2.5 IU/ml was taken as the cut off value for determining the positive sera with the VNAb technique. The possibility that clinicians might use the RAT as a simple means to determine sero-conversion at the end of the post-exposure treatment of patients is discussed.

Free kappa and lambda light chain levels in the cerebrospinal fluid of patients with multiple sclerosis and other neurological diseases

Free kappa and lambda light chains were assayed by particle-counting immunoassay in cerebrospinal fluid (CSF) from patients with various neurological disorders. Detection limits were 25 and 50 ng/ml, respectively. Values of free kappa chain were higher than 50 ng/ml (upper reference limit) in 155 of 191 (81%) multiple sclerosis (MS) patients, in 100 of 168 (60%) patients with central nervous system (CNS) infections but in 41 of 217 (19%) patients with other neurological disorders. Free kappa chains were also assayed in 273 matched sera. The mean concentration in the control group (1.58 micrograms/ml; SD: 0.41) did not differ significantly from those in MS sera (1.63 micrograms/ml; SD: 0.43). The free kappa chain index was increased in 86% of MS patients and in 40% of patients with CNS infections. Regarding free lambda chains, CSF values were higher than 240 ng/ml (upper reference limit) in most neurological disorders (50-100%). However, the use of a lambda chain index increased the specificity of the assay as this index was higher than the upper reference value in 86% of MS patients and in only 23% of patients with infectious diseases. In MS, high levels of free kappa and lambda indices correlated significantly (P less than 0.01) with either the presence of oligoclonal bands or a high IgG index. Local synthesis of free light chains is an additional marker of an ongoing immune response within the CNS, especially in MS.

Human immune response to allergens of house dust mite, Dermatophagoides pteronyssinus. Isotypic analysis of antibodies in atopic and non-atopic subjects

Specific antibodies isolated by immunoabsorption on four main insolubilized allergens from Dermatophagoides pteronyssinus (DPT) had the following isotypic distribution: in 16 atopic patients, 52% IgG, 40% IgM, 8% IgA, 0.1% IgE and, in 12 non-atopic individuals, 48% IgG, 46% IgM, 6% IgA, 0.03% IgE. The ratios between geometric means of antibody values in each class (atopic vs non-atopics) were 2.4 for IgG, 2.0 for IgM, 2.8 for IgA and 66.7 for IgE. The amount of anti-DPT antibodies in IgG subclasses did not follow the usual distribution of total IgG subclasses, i.e., IgG1 greater than IgG2 greater than IgG3 greater than IgG4. In atopics the order was IgG2 greater than IgG1 greater than IgG4 greater than IgG3 and in non-atopics, IgG4 greater than IgG1 = IgG2 greater than IgG3 although 6/12 of the latter had no detectable (less than 0.5 micrograms/ml plasma) IgG4.

Latex allergosorbent test (LAST): a new immunoassay for specific IgE with latex particles

We describe a two-step latex (Lx) agglutination assay for the titration of specific anti-Dermatophagoides pteronyssinus IgE. The samples are first incubated with allergen-coated Lx of 2.3 microns diameter. Bound IgE is digested by pepsin and then titrated by its agglutinating activity on 0.8 micron Lx particles coated with antihuman Fc epsilon rabbit F(ab')2. This latex allergosorbent test detects 100 pg of specific IgE per milliliter and does not depend on the concentration of total IgE. Owing to a tenfold increase in the allergosorbent surface, no competition with the binding of specific anti-D. pteronyssinus IgG is observed. Pepsin digestion eliminates potential interferences caused by autoantibodies against IgE. A good correlation (r = 0.92) is found with Phadebas RAST on a series of 91 samples. The latex allergosorbent test does not make use of radioisotopes and can be performed in less than 6 hours.

Jacalin: isolation, characterization, and influence of various factors on its interaction with human IgA1, as assessed by precipitation and latex agglutination

An IgA1-specific lectin, Jacalin, was isolated from dried seeds of the jackfruit, Artocarpus integrifolia, by affinity binding to IgA1-Sepharose and elution with D-galactose. Jacalin is a glycoprotein with two non-covalently bound subunits (15 and 18 K). Interactions between Jacalin and human Igs were studied by precipitation in gel and in solution, and by agglutination of IgA1-coated latex by Jacalin. Jacalin precipitated only with IgA1-containing samples, including monomers, polymers, monoclonal, polyclonal and secretory IgA1, but not IgA2 of both A2m(1) and A2m(2) allotypes, nor with IgG1, 2, 3 and 4, IgM, IgD, and IgE; after neuraminidase treatment, only IgA1 and IgD were precipitated. Jacalin had a relatively broad pH range of activity in both precipitation and agglutination of IgA1-latex. Bivalent metal cations (Ca, Mg, Mn, Cu, Zn, Co, Cd), EDTA, Triton X-100, Tween-20, Na deoxycholate and ionic strength did not influence these reactions. Na dodecylsulphate, guanidine and urea inhibited the reactions whereas NP-40 rather enhanced them. Among 39 types of sugar tested, 10 displayed inhibitory activity, decreasing in the following order: p-nitrophenyl-alpha-D-galactopyranoside, 1-O-methyl-alpha-D-galactopyranoside, D-melibiose, p-nitrophenyl-beta-D-galactopyranoside, GalNAc, stachyose, 1-O-methyl-alpha-D-mannopyranoside, D-galactose, D-galactosamine and 1-O-methyl-alpha-D-glucopyranoside. IgA1, treated with neuraminidase or not, but not the other human Igs, was also an excellent inhibitor of agglutination, being more powerful than the best sugars studied. Only neuraminidase-treated IgD was also inhibitory, but less so than IgA1. Jacalin preferentially bound to alpha-linked non-reducing D-galactose. The configuration of OH-groups at C-2, C-4 and C-6 of D-galactose was important for the reaction. Jacalin recognizes terminal Gal beta 1-3GalNac-, as in the IgA1-hinge, and/or GalNAc-, but not Gal beta 1-4GlcNAc-, nor Gal beta 1-6GlcNAc-, nor their sialylayted extensions. Latex agglutination and its inhibition assay are particularly well suited for the study of these lectin-glycoprotein interactions.

Immunoassay of hepatitis B surface antigen by particle counting after pepsin digestion

Particle counting immunoassay is based on latex agglutination, the reaction being measured by instrument counting of the particles remaining unagglutinated. Most interference which generally affects latex agglutination can be avoided by pepsin digestion of the sample, provided the antigen (Ag) of interest resists pepsin, which is the case of the hepatitis B surface antigen (HBsAg). Pepsin treatment has the additional advantage of inactivating antibodies and so releasing the Ag from immune complexes. We have set up an assay of HBsAg, proceeding in a prototype of Impact Instrument (Acade Diagnostic Systems, Belgium) at a rate of 60 samples.h-1 and a total running time of 2 or 4 h. This assay was compared with Abbott radioimmunoassay (RIA) in 706 consecutive patients (A) and 31 selected sera for which values close to the cut-off had been obtained by RIA (B). In A, 38 sera were found positive and 668 negative by both methods. In B, RIA after neutralization classified the samples as positive (n = 14), negative (n = 14), or dubious (n = 3). Complete agreement between latex and RIA was achieved for nine positive, 12 negative, and two dubious samples. Of five RIA-positive samples, two were classified as latex-negative and three as dubious in the latex assay. One sample dubious in RIA was found latex-positive and two RIA-negative samples were found, respectively, latex-positive and dubious; when retested after pepsin digestion, the first of them became RIA-positive.(ABSTRACT TRUNCATED AT 250 WORDS)

Lymphocytic meningoradiculitis and encephalomyelitis due to Borrelia burgdorferi: a clinical and serological study of 18 cases

Clinical features of 18 patients with either lymphocytic meningoradiculitis (n = 17) or chronic encephalomyelitis (n = 1) due to Borrelia burgdorferi are reported. Arthropod bites were recorded in only seven patients. High titres of anti B burgdorferi antibodies were detected in sera from all patients and in CSF from 12 out of 17 patients tested. All patients had CSF abnormalities especially pleocytosis and oligoclonal bands. A falsely positive syphilitic serology was observed in the CSF from the patient with encephalomyelitis.

The use of particle counting immunoassay for the diagnosis of neurological disease

Particle counting immunoassay (PACIA) is applied to the determination of proteins at trace levels in normal and pathological cerebrospinal fluid (CSF) samples. Performance characteristics for the assays are given and the results for immunoglobulins (Igs) expressed as Ig indices. Ig profiles characteristic of various neurological disorders have been studied, and anti-herpes antibodies detected using an agglutination inhibition method. Ferritin, C-reactive protein and the brain protein S-100 have also been studied.

The human immune response against major allergens from house dust mite, Dermatophagoides pteronyssinus. II. Idiotypic cross-reactions of allergen-specific antibodies

Antisera were prepared in rabbits against the idiotypic (Id) determinants of antiallergen antibodies. These antibodies were isolated from the plasma of 10 unrelated patients by immunoabsorption. Three major allergens isolated from the house dust mite, Dermatophagoides pteronyssinus (DPT), were used. The anti-Id antisera were rendered specific by successive absorption on insolubilized allergens, IgG and IgM from a pool of human sera and Ig from the donor after removal of anti-DPT antibodies by absorption. Anti-Id antibodies raised essentially against IgG antibodies were found to inhibit the agglutinating activity of both IgG and IgM anti-DPT antibodies toward allergen-coated latex. These anti-Id antibodies were also able to inhibit partly the binding of radiolabeled allergen to IgE anti-DPT antibodies. Matching the anti-Id antisera with the various individual anti-DPT antibodies revealed an Id cross-reactivity of about 71% for IgG, 61% for IgM and 62% for IgE. A second and predominant type of anti-Id antibodies recognized bystander idiotopes as the allergen did not inhibit Id-anti-Id reaction. These idiotopes were apparently more specific to individuals (private) as the anti-DPT antibodies of a given patient did not agglutinate latex particles coated with anti-Id antibodies prepared against Id of another patient.

Comparison of human lactoferrins from milk and neutrophilic leucocytes. Relative molecular mass, isoelectric point, iron-binding properties and uptake by the liver

Human lactoferrins isolated from neutrophilic leucocytes and milk by CM-Sephadex chromatography were similar in Mr (76000) and pI (8.7). Upon acidification, both proteins released their two Fe3+ ions/molecule in a similar biphasic way. Both proteins intravenously injected into mice were cleared from plasma at the same rate. The maximal uptakes by the liver, which occurred 5 min after injection, were inhibited to the same extent by milk lactoferrin used as a competitor.

Immunoglobulin E assayed after pepsin digestion by an automated and highly sensitive particle counting immunoassay: application to human cord blood

We describe in this article a fully automated, universal assay for serum IgE after pepsin digestion of the sample and subsequent assay of the released Fc" epsilon fragment by particle counting immunoassay (PACIA). The sensitivity and the range of the assay were easily modulated by changing the concentration of dextran in the reaction medium. In the application to cord serum, the sensitivity reached 0.1 IU/ml in 30 min incubation time and with a throughput of 50 analyses per hour. Within-day and between-day coefficients of variation did not exceed 7.6% for IgE levels covering a wide range of the standard curve. Dependable accuracy was demonstrated by linearity tests, analytical recoveries (89% to 112%), and correlation with PRIST on 48 samples from children ages 1 to 14 yr (y = 0.97x + 5.92; r = 0.987). Minor discrepancies between the two methods were attributed to a slight serum effect in PRIST. PACIA applied to 348 cord serum samples demonstrated a statistically significant influence of sex and race on the cord IgE level. In European neonates boys had significantly (p = 0.019) higher geometrical mean cord IgE levels (n = 142; 0.46 IU/ml; range less than 0.10 to 30 IU/ml) than girls (n = 146; 0.33 IU/ml; range less than 0.10 to 8.0 IU/ml), which was attributed to a predominance of boys (chi 2 = 4.29; p less than 0.05) having more often elevated cord IgE (less than 1.20 IU/ml) than girls. Neonates of African-Asian origin had significantly (p less than 0.00005) higher cord IgE levels (n = 60; 1.05 IU/ml; range less than 0.10 to 125.0 IU/ml) than European neonates (n = 288; 0.39 IU/ml; range less than 0.10 to 30.0 IU/ml).

Monitoring and tentative diagnosis of herpetic encephalitis by protein analysis of cerebrospinal fluid. Particular relevance of the assays of ferritin and S-100

The cerebrospinal fluid (CSF) of 9 patients with herpetic encephalitis was analyzed by particle counting immunoassay of ferritin, S-100, immunoglobulins, anti-herpes antibodies and immune complexes and by electrophoresis for the detection of oligoclonal bands. The main conclusions are: first, the simultaneous increase of both ferritin and S-100 in the presence of symptoms of encephalitis suggests strongly the infection is herpetic; second, high and increasing levels of S-100, probably related to the extent of the necrotic process, indicate a poor prognosis. In addition, 8-14 days after onset, locally produced anti-herpes antibodies were detectable, the IgG index increased and oligoclonal bands became visible.

Immunoglobulin E in aqueous humour

The level of immunoglobulin E (IgE) was determined in the aqueous humour (AH) and serum by particle counting immunoassay (limit of sensitivity: 0.2 IU ml-1). This level in the AH was below 0.75 IU ml-1 in case of senile cataract (n = 22) and ranged from this assumed normal value to 550 IU ml-1 in case of uveitis (n = 37), Fuchs' cyclitis (n = 11), intraocular tumour (n = 7) and perforating ocular injury (n = 6). To know whether the IgE increase was related to a possible local production the AH/serum concentration ratio for IgE was calculated and divided by that for albumin. Values higher than 0.60 were considered as suggestive of a local synthesis and were observed in 31 of the 37 samples examined.

Secretion of immunoglobulins and plasma proteins from the jejunal mucosa. Transport rate and origin of polymeric immunoglobulin A

Parameters of secretion of IgA and several other plasma proteins from the jejunal mucosa were investigated in 11 individuals who had a normal distribution of Ig-containing cells in the lamina propria and in one patient who was totally deficient in jejunal IgA and IgM plasmacytes. Jejunal samples were collected during segmental gut perfusion. The following results were obtained: (a) The secretion of polymeric IgA (p-IgA, mean equals 217 micrograms/40 cm per min) exceeded those of albumin (132 micrograms), IgG (35 micrograms), and monomeric IgA (m-IgA, 15 micrograms, or 6.4% of total IgA). About 35% of IgA was IgA2 in the jejunal secretion, compared with approximately 23% in serum. This closely corresponds to the 35 and 24% of IgA2 plasmocytes in jejunal mucosa and peripheral lymph nodes, respectively. (b) For each protein, a relative coefficient of excretion (RCE) was calculated (jejunum to serum concentration ratio expressed relative to that of albumin). RCEs of 1.41 for orosomucoid, 1.0 for albumin, 0.83 for IgG, and 0.74 for IgE and, in the deficient patient, of 0.64 for m-IgA and 0.016 for IgM were obtained. This was inversely related to the molecular weight of these proteins and indicated their predominantly passive transport into the jejunum. However, in normal individuals, the RCE of transferrin (approximately 1.11 greater than 1, P greater than 0.05), alpha 2-macro globulin (approximately 0.77), m-IgA (approximately 1.98), and p-IgA (approximately 218) exceeded the value expected from simple seepage from plasma, thus pointing to an additional role of either local gut synthesis and/or active transepithelial transport. (c) Approximately 98% of p-IgA, approximately 99% of IgM, and approximately 68% of m-IgA in jejunal secretions were derived from local production in the gut wall, as determined by 125I-p-IgA specific activities and/or by comparison between the RCE values of the deficient patient to the values of controls. Therefore, the jejunal production of p-IgA (approximately 312 mg/d per 40 cm vs. approximately 54 mg/d from bile) contributes the majority of upper intestinal IgA in humans. The active transport of plasma p-IgA across the intestinal mucosa (approximately 0.08 mg/40 cm per kg per d) contributes less than 2% of the total amount of p-IgA (4.5 mg/kg per d) that is cleared daily from plasma.

Typing of subclasses and light chains of human monoclonal immunoglobulins by particle counting immunoassay (PACIA)

The subclasses of monoclonal IgGs and IgAs were identified by particle-counting immunoassay. The principle of the test is the inhibition of the agglutinating activity of either specific antisera or monoclonal antibodies (for IgA only) on latex particles coated with a monoclonal IgG or IgA of known subclass. The feasibility of assay of polyclonal Ig subclasses was demonstrated. However, the anti-IgG2 antiserum cross-reacted with an allotype (nG4m(b)) of IgG4. The possibility of typing monoclonal Igs for light chains by the same technique was also demonstrated. Results are obtained in 30 min, and the method requires only small amounts of purified immunoglobulins (Igs) and antisera or monoclonal antibodies.

An automated particle counting immunoassay (PACIA) for determination of blocking antibodies against timothy grass pollen in sera from desensitized allergics

An automated particle counting immunoassay (PACIA) for measurement of blocking antibodies (antigen neutralizing capacity) against timothy grass pollen extract in sera from desensitized allergics is described. Latex particles coated with F(ab')2-anti-timothy are agglutinated by timothy. Serum containing anti-timothy antibodies inhibits the agglutination. Non-agglutinated particles are counted in a modified AutoCounter. Nineteen of 20 sera from timothy allergics who had undergone immunotherapy with purified timothy extract for 30 weeks, showed significant agglutination-inhibition. None of 42 normal human sera gave significant inhibition. The inhibiting antibody could be removed by absorption with protein A and was thus of non-IgE nature, i.e. blocking antibody. The results obtained correlated statistically significantly with those found with a double-antibody method (rS = 0.62, n = 20, t = 3.35, P less than 0.01) and with the cumulated dosage of timothy allergen extract administered to the individual patient (rS = 0.56, n = 20, t = 2.87, P less than 0.02). Between-assay coefficient of variation was from 6.4% to 18.3%. The capacity is 40 samples per hour. The method has also been applied to measurement of blocking antibodies to honey bee and wasp venom.

Isotypic and allotypic specificity of mouse rheumatoid factors

The specificity of polyclonal mouse rheumatoid factors (RF) was analyzed by competition experiments with heat-aggregated mouse IgG subclasses. The RF spontaneously produced by three normal mouse strains (129/Sv, CBA/Ht, and C57Bl/6) and by two strains with autoimmune diseases (MRL/l and NZB) were found to consist of distinct non-cross-reactive antibody subpopulations each specific for one IgG subclass. The sera of the normal strains contained IgG1- and IgG2a-specific RF. The autoimmune strains produced an additional variety of RF that was specific for The autoimmune strains produced an additional variety of RF that was specific for IgG2b. Also, the RF secreted by spleen cells of various normal strains after in vitro polyclonal activation with lipopolysaccharide could be resolved into distinct subpopulations specific for IgG1 or IgG2a. These results were confirmed by the analysis of monoclonal RF derived from BALB/c, C57Bl/6, CBA/Ht, and 129/Sv mice: of 73 hybridomas with RF activity, 71 displayed a strict subclass specificity. The subclass predominantly recognized depended on the origin of the spleen cells used to generate the hybridomas. After polyclonal activation in vitro, a broad spectrum of different specificities was obtained with 16 RF specific for IgG1, 13 for IgG2a, and 4 for IgG2b. In contrast, 27 of 28 monoclonal RF derived from 129/Sv and BALB/c mice without prior polyclonal activation were specific for IgG2a, and of these 75% were allotype specific since they failed to react with IgG2a of the b allotype. These results demonstrate the importance of subclass specificity in the production of RF in vivo. With the exception of the IgG2b-specific clones, all these monoclonal RF reacted preferentially with heat-aggregated or antigen-bound IgG. Among the hybridomas generated by the fusion of in vitro polyclonally activated spleen cells of 4-wk-old mice, the frequency of clones with RF activity was at least 40 times higher than that of clones specific for mouse IgM, human IgG, ovalbumin, and hen lysozyme.

Particle counting immunoassay of immunoglobulin E antibodies after their elution from allergosorbents by pepsin: an alternative to the radioallergosorbent test

The absorption of specific antibodies on allergen-coated cellulose discs, followed by pepsin digestion to release the IgE Fc" fragment, which is then assayed by particle counting immunoassay (PACIA), is a new practical and reliable method to quantitate IgE antibodies and to standardize allergens. The coefficient of variation of repeated assays does not exceed 12.8% and the correlation coefficient with RAST was r = 0.96. Some discrepancies could be explained by differences in the antiserum specificities and the presence of anti-IgE autoantibodies. The determination of IgE antibodies by PACIA offers the following advantages: (1) no radioisotopes; (2) stability of reagents, since antibody-coated latex particles and the standards keep their activity for more than 1 yr; (3) low cost of reagents due to ease of preparation --PACIA does not require purified antibodies to measure IgE but only F(ab')2 fragments of the IgG fraction of the anti-IgE antiserum to coat latex; (4) avoidance of nonspecific absorption of the labeled anti-IgE on the solid phase; (5) prevention by elution of the inaccuracies observed in RAST at very high titers of IgE antibodies; (6) expression of the results in international units per milliliter to calculate the ratio of specific IgE Ab vs total IgE, with a high ratio suggesting that the patient is sensitive to a few allergens; (7) standardization of allergenic extracts; and (8) the particular specificity of the anti-IgE antiserum directed against a heat- and protease-resistant fragment of IgE.